5.05 Inhalation Injury

Presentation

The patient was trapped in an enclosed space for some time with toxic gas or fumes produced by a fire, leak, evaporation of solvent, chemical reaction, fermentation of silage, etc., and comes to the ED complaining of some combination of coughing, wheezing, shortness of breath, irritation or running of eyes or nose, chest or abdominal pain, or skin irritation. More severe symptoms include confusion and narcosis. Symptoms may develop immediately or after a lag of as much as a day. On physical examination, the victim may smell of the agent or be covered with soot or burns. Inflammation of the eyes, nose, mouth, or uppe rairway may be visible, while pulmonary irritation may be evident as coughing, ronchi, rales, or wheezing, although these signs may also take up to a day to develop.

What to do:

Separate the victim from the toxic agent by removing clothes, hosing down, or showering with soap and water.

Make sure the victim is breathing adequately, and then add oxygen at 6 to 12 liters per minute. Oxygen helps most inhalation injuries, and is essential in treating carbon monoxide poisoning.

Look for evidence that may help identify the exposure: Was there a fire? What was burning? What was the estimated length of exposure? Was it an open or a closed space? What is the status of other victims? Was there an associated blast? What material is on the victim? What does he smell of? What are his current signs and symptoms? Is there soot in the posterior pharynx or singed nasal hairs? There may be evidence of a specific toxin which calls for a specific antidote (e.g., muscle fasiculations, small pupils, and wet lungs may imply organophosphates which should be treated with atropine).

Unless the patient is asymptomatic, obtain a chest x ray and arterial blood gases (record the percentage of oxygen being inhaled). An increased alveolar-arterial PO2 difference may be the earliest sign of pulmonary injury; but even if the CXR and ABGs are normal, they can serve as a baseline for evaluation of later pulmonary problems. Consider obtaining a carboxyhemoglobin (COHgb) level, if only as a marker of other combustion products. Obtain a cyanide (CN) level too if there is any suspicion.

Determine if there are significant pre-existing conditions such as cardiac or cerebral vascular disease, chronic obstructive pulmonary disease, asthma, or other chronic illness.

If the patient has difficulty breathing or any x ray or blood gas abnormality suggesting acute pulmonary injury, he should be kept on oxygen and admitted to the hospital, even if only overnight. Wheezing and bronchospasm may be allergic reactions and respond to conventional doses of aerosolized bronchodilators, but, if not promptly reversible, are probably a sign of pulmonary injury.

If no signs or symptoms of inhalation injury develop, or all have resolved in one hour, it may be safe to send the patient home, with instructions to return for reevaluation the next day or sooner if any pulmonary signs or symptoms occur (coughing, wheezing, shortness of breath).

Repeat the patient's vital signs and physical exam, and consider repeating ABGs, and CXR in 12 to 24 hours, looking for any changes indicative of late pulmonary injury.

What not to do:

Do not assume the patient is all right following an inhalation injury simply because there are no symptoms and no ABG or CXR abnormalities evident in the first few hours. Some agents produce pulmonary inflammation which develops over 12 to 24 hours.

Do not wait for carboxyhemoglobin levels before giving 100% oxygen for suspected carbon monoxide poisoning. Begin oxygen as soon as possible. One hundred percent oxygen (which requires a tight-fitting mask and a reservoir for administration) will reduce the half-life of carboxyhemoglobin from 6 to 1.5 hours.

Do not insist on having the patient breathe room air for a long period before obtaining ABGs. If the oxygen is helping, its withdrawal is a disservice, and the alveolar-arterial PO2 gradient can still be estimated on supplemental oxygen.

Discussion

One category of inhalation injury is caused by relatively inert gases, such as carbon dioxide and fuel gases (methane, ethane, propane, acetylene) which displace air and oxygen,producing asphyxia. Treatment consists of removing the victim from the gas and allowing him to breathe air or oxygen, and attending to any damage caused by the period of hypoxia (myocardial infarction, cerebral injury).

A second category of inhalation injury is from irritant gases: ammonia (NH3), formaldehyde(HCHO), chloramine (NH2Cl), chlorine (Cl2), nitrogen dioxide (NO2) and phosgene (COCl2), which, when dissolved in the water lining the respiratory mucosa, produce a chemical burn and an inflammatory response. The first gases listed, being more soluble in water, tend to produce more upper airway burns, irritating eyes, nose, and mouth, while the latter gases, being less water soluble, produce more pulmonary injury and respiratory distress.

A third category of inhalation injury includes gases which are systemic toxins, such as carbon monoxide (CO), hydrogen cyanide (HCN), and hydrogen sulfide (H2S), all of which interfere with the delivery of oxygen for cellular energy production, and aromatic and halogenated hydrocarbons, which can produce later liver, kidney, brain lung, and other organ damage

A final category of inhalation injury is allergic, in which inhaled gases, particles or aerosols produce bronchospasm and edema much like asthma or spasmodic croup.